1. Field of the Invention
The present invention relates to an eyepiece lens system which has a long eye relief and a wide visual field, and is to be used in telescopes, binocular telescopes and so on.
2. Description of the Prior Art
An eyepiece lens system disclosed by U.S. Pat. No. 1,478,704 is known as a conventional example of eyepiece lens systems which have apparent visual fields on the order of 70.degree.. Further, an eyepiece lens system disclosed by Japanese Patent Kokai Publication No. Hei 6-109,983 is known as another conventional example of eyepiece lens systems which have apparent visual fields on the order of 72.degree. and eye relieves on the order of 1.3 f (f represents a focal length of an eyepiece lens system as a whole). Furthermore, an eyepiece lens system disclosed by Japanese Patent Kokai Publication No. Sho 56-85,723 is known as still another conventional example of eyepiece lens systems which has apparent visual fields exceeding 80.degree..
The conventional examples mentioned above have defects which are to be described consecutively below:
The conventional example proposed by the U.S. Pat. No. 1,478,704 has a simple composition which comprises a small number of lens elements, but a short eye relief of 0.6 f to 0.68 f, whereby the eyepiece lens system will inevitably has a long focal length when it is configured so as to have a long eye relief. In addition, this eyepiece lens system has an apparent visual field which is as narrow as 70.degree..
Further, the eyepiece lens system disclosed by Japanese Patent Kokai Publication No. Hei 6-109,983 has an eye relief of 1.27 f to 1.30 f and is sufficiently compact. However, this eyepiece lens system has an apparent visual field of 72.degree. which is rather narrow or not so much larger than those of general wide-field binocular telescopes (having field angles of 65.degree. and larger).
Furthermore, the conventional example proposed by Japanese Patent Kokai Publication No. Sho 56-85,723 produces aberrations within a pupil thereof and allows a visual field thereof to be eclipsed.